164 
PALEONTOLOGY OF NEW YORK. 
Leiopteria Dekayi. 
PLATE XIX, FIG. 1 ; PLATE XX, FIGS. 16-18 ; and PLATE LXXXVIII, FIGS. 5-10. 
Leicrpteria Dekayi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 19, fig-. 1 ; pi. 20, figs. 
16-18, (19 in error). Jan., 1883. 
Shell of medium size, sub-rhomboidal in general form; body narrowly ovate, 
oblique; length about equal to the height; anterior margin nearly vertical 
for one-third the length of the shell, thence broadly rounded over the basal 
margin and abruptly recurved at the post-basal extremity. 
Left valve convex, gibbous on the umbo. Right valve smaller and less 
convex; the limitation of the wing not strongly defined. 
Hinge-line straight, length a little less than the length of the shell 
measured from the anterior side of the beak to the extremity of the wing. 
Beaks anterior, acute, prominent, inclined forward. Umbonal region 
gibbous above, regularly convex below, subtending an acute angle. 
Ear bending downward, with a strong fold in the upper part, limited by 
a broad undefined sulcus and shallow byssal sinus. Wing triangular, flat, 
defined by the abrupt retral bending of the striae and a depressed line along 
the post-cardinal slope; margin concave; extremity acute. 
Test thin, marked by fine regular concentric striae, which at unequal 
intervals are crowded into fascicles, giving an undulated aspect to the surface 
of the cast; in old specimens, more crowded on the anterior side and ear, 
and on the wing usually regular, sometimes becoming a little fasciculate on 
the margin. 
This description of the surface is taken from casts or partial casts which 
preserve more or less the surface markings. In a few younger specimens 
from the shales, the surface shows fine regular striae which gradually become 
fasciculate as the shell increases in size. 
Ligamental area narrow, marked by fine striae ; below this area is a narrow 
oblique fold or lateral tooth. 
The three specimens figured on plate xx, have respectively the following 
dimensions: length 37, 31, and 29 mm., height 37, 30, and 30 mm., hinge- 
